The present invention relates to a chip resistor in which a resistor film is provided on a chip-type insulating substrate and a manufacturing method thereof. More specifically, the present invention relates to a chip resistor and a manufacturing method thereof, wherein the manufacturing process is simple to enable economical production, while high-performance properties can be obtained.
Conventional chip resistance element include a thick-film resistor wherein electrodes and resistance element are formed by printing and firing, and a thin-film resistor wherein electrodes and resistance element are formed by sputtering. Though there are differences in the thick film and the thin film, and in the upper and lower sides of the resistance element and the top electrodes, the structures thereof are almost the same, and for example, are as shown in FIG. 14. That is to say, in FIG. 14, a pair of electrodes 2, 3 are formed of top surface electrodes 21, 31, back surface electrodes 22, 32, and side surface electrodes 23, 33 connecting these top and back surface electrodes, at both of the opposite ends of an insulating substrate 1 comprising alumina or the like, and a resistance element 4 is formed on the insulating substrate 1, so as to be connected to the both electrodes. A protective film 5 is also formed in one to three layers on the surface side of the resistance element. The thick film is formed in a thickness of, for example, 5 to 10 xcexcm, and the thin film is formed in a thickness of, for example, 0.1 to 0.5 xcexcm.
The thick-film resistor is obtained by applying a paste material by printing or the like using a glass or a resin, and firing the material at 600 to 900xc2x0 C. (in the case of glass) or curing this at 200 to 240xc2x0 C. (in the case of resin), to thereby form each layer. As an electrode material, a metal paste of an Ag type in which Pd is added to Ag, or an Au type in which Au is used as a main component is used. As a resistance element material, there is used one obtained by mixing Ag or the like in ruthenium oxide (RuO2) in order to have a necessary value of resistance, and forming a paste by a glass or a resin. Also, the thin-film resistor is obtained by forming a film from a metal material by sputtering or the like and patterning this film. As the electrode material, Al, Ni, Cr or Cu is used, and as the resistance element material, an Nixe2x80x94Cr alloy or the like is used.
Thus, the manufacturing processes are different in that one is provided by printing and heat processing, and the other is provided by sputtering. Also these are different in view of equipment such as printing apparatus or sputtering apparatus, and the production line is quite different. Therefore, use of the both films together makes the production process complicated, and it is practically difficult.
As described above, there is a thick-film resistor or a thin-film resistor in chip resistor, and the thick-film resistor has an advantage in that the production equipment is very cheap, and such a resistor itself can be manufactured economically. However, since the resistance element is obtained by making a paste of ruthenium oxide, the accuracy of resistance value is poor based on the heterogeneous composition, the non-uniform thickness at the time of application, and a difference in dosage of Ag or the like in order to adjust the resistance value, and there is a problem in that it is inferior in performance, such as poor noise performance, as well. On the other hand, the thin-film resistor is excellent in the accuracy of resistance value and noise performance, but there is a problem in that expensive sputtering apparatus has to be used, and its production takes time, thereby making such a resistor considerably expensive.
On the other hand, if the thick film and the thin film are combined, not only the production line becomes complicated as described above, but also there are problems in that when a thick film is formed on a thin film, adhesion decreases, contact resistance increases, and the quality thereof is not uniform, though there is no problem in adhesion when a thin film is formed on a thick film.
In order to solve these problems, it is an object of the present invention to provide a chip resistor and a manufacturing method thereof, wherein accuracy of resistance value is improved, and productivity is improved, while increasing resistance characteristics such as noise performance.
It is another object of the present invention to provide a chip resistor capable of surface mounting, while improving a connection between a resistance element and electrodes, in case that a thin-film is used as the resistance element, and a thick-film is used as the electrodes.
The chip resistor according to the present invention comprises: an insulating substrate; a resistance element formed by a thin film so as to extend from one end to the opposite other end of the insulating substrate on the surface thereof; top surface electrodes formed by a thick film at the opposite ends of the insulating substrate, so as to be connected to the opposite ends of the resistance element, respectively; back surface electrodes formed by a thick film on the backside of the insulating substrate, the back surface electrodes being electrically connected to the top surface electrodes via thick-film electrodes, respectively; and a protective film provided on the surface of the resistance element.
The thick film herein stands for a film formed thick by applying materials of an electrode or a resistance element in a paste form and firing or curing this paste, and the thin film stands for a film formed thin by directly forming a metal film or the like by sputtering or the like.
By having such a construction, since a resistance element is formed by a thin film, the resistance performance such as accuracy of resistance value and noise performance can be obtained with high accuracy. On the other hand, since electrodes and the like are formed by a thick film, the production process becomes simple, enabling economical production.
Specifically, the construction may be such that each of the top surface electrodes comprises a first top surface electrode and a second top surface electrode, and each of the opposite ends of the resistance element is clamped in a sandwich construction by the first top surface electrode and the second top surface electrode provided on the surface of the insulating substrate, with a part of each of the opposite ends of the resistance element removed so that the first top surface electrode and the second top surface electrode come in direct contact with each other, and the second top surface electrode and each of the back surface electrodes are connected by a side surface electrode formed by a thick film on the side of the insulating substrate, respectively.
By having such a construction, a part of the resistance element is removed so that the first top surface electrode and the second top surface electrode come in direct contact with each other, and the first top surface electrode and the second top surface electrode are both formed by a thick film. Hence, these have excellent adhesion. The resistance element sandwiched therebetween has excellent adhesion with the first top surface electrode, since it is a thin film on a thick film, and can be also connected electrically with the second top surface electrode via the first top surface electrode with low resistance. As a result, even if a side surface electrode or a bump electrode is provided in a thick film on the second top surface electrode, both of the second top surface electrode and the side surface electrode are similarly thick film and have good adhesion. Hence, an electrode structure having excellent contact state can be obtained.
Another specific construction may be such that the resistance element formed by a thin film comprises a laminated structure having a first layer and a second layer, each of the opposite ends of the resistance element clamps the top surface electrode between the first layer and the second layer in a sandwich construction, and the first layer is provided with an exposed portion of the insulating substrate so that the top surface electrodes come in direct contact with the insulating substrate, and the second layer is formed such that the top surface electrode has an exposed portion not covered with the second layer.
By having such a construction, the top surface electrode is provided so as to come in direct contact with the insulating substrate through the exposed portion formed in the first layer, and hence, these have good adhesion. Moreover, since the top surface electrode and the second layer have good adhesion, since these are in the relation of a thin film on a thick film, and both resistance elements have good adhesion, since these are thin films. Thus, the top surface electrode and the resistance element are connected with good adhesion.
Moreover, another specific construction is such that the resistance element is formed on the insulating substrate, each of the top surface electrode is formed on the opposite ends of the resistance element, and thin-film top surface electrodes are formed so as to cover a part of each of the top surface electrode and a part of the resistance element at the opposite ends, and the exposed portion of each of the top surface electrodes and each of the back surface electrodes is connected by a side surface electrode provided by a thick film on the side of the insulating substrate. That is, in the above construction, by having such a construction that the second layer of the resistance element is provided only at the opposite ends, or by using an electrode material as the material provided at the opposite ends, the adhesion can be improved from the same reason as above.
As further another specific construction, there can be mentioned a construction, in which through holes are formed at the opposite ends of the insulating substrate, and through hole electrodes are formed by a thick film in the through holes so as to respectively connect each of the top surface electrodes and each of the back surface electrodes, and the resistance element is formed so that the opposite ends of the resistance element overlap on the top surface electrodes.
By having such a construction, while using a thin-film resistance element and thick-film top surface electrodes, the top surface electrodes can be connected to the back surface electrodes by thick films, without overlapping the top surface electrodes on the thin-film resistance element, thereby enabling connection with good adhesion. Moreover, a protective film can be formed on the top surface electrodes, so the material that is not easily diffused into the resistance element can be used for the top surface electrodes, without taking into consideration corrosion due to solder plating.
By forming each of the through holes such that the longitudinal section thereof is not exposed to the side of the insulating substrate, a fillet-less construction can be obtained at the time of soldering for mounting, thereby enabling reduction in the mounting area.
By having such a construction that the longitudinal section of each of the through holes is exposed on the side of the insulating substrate, and each of the through hole electrodes is substantially filled in the through holes, to thereby expose each of the through hole electrodes substantially in a flat face on the side of the insulating substrate, the thin-film resistance element and the thick-film electrode can be connected with good adhesion, while keeping the same shape as that of the structure for connecting the top surface electrodes and the back surface electrodes with a conventional side surface electrodes.
Further another aspect of the chip resistor according to the present invention comprises: a pair of first top surface electrodes formed by a thick film provided on the surface of the opposite ends of an insulating substrate; a thin-film resistance element provided on the substrate so that the opposite ends thereof respectively overlap on the first top surface electrodes; a pair of second top surface electrodes formed by a thick film provided on the first top surface electrode exposed by removing a part of the resistance element and on the surface of the opposite ends of the resistance element; a protective film provided between the pair of second top surface electrodes on the surface of the resistance element; and bump electrodes provided on the surface side of the second top surface electrodes so as to be electrically connected to the second top surface electrodes, respectively.
By having such a construction, there is no such a problem that the resistance value changes due to the forming situation of solder fillets on the side surface electrodes. In addition, the chip resistor can be mounted in a very small area, without protruding from the flat surface area of the chip resistor.
A manufacturing method of a chip resistor according to the present invention comprises the steps of: (a) providing a pair of first top surface electrodes at the opposite ends of an insulating substrate by a thick-film forming method; (b) forming a resistance element film on the first top surface electrodes and the exposed insulating substrate by a thin-film forming method, and performing patterning so as to expose a part of each of the first top surface electrodes and to have a desired shape to thereby form a resistance element; and (c) providing a pair of second top surface electrodes by a thick-film forming method, so as to overlap on the pair of first top surface electrodes.